cbh az swings 25sep12
last updated 29sep12
Azimuth swings were done with the cband high receiver on 25sep12.
The setup was:
The data processing for each box:
- az 270-630 and back at +/- .35deg/sec
- cloudy but no rain. data taken around 5 pm.
- dome at za=15deg
- mock spectrometer with 7 boxes covered 6 to 7 GHz
- 172MHz bw, 8192 channels per box
- .1 sec sampling (averaged to 1 second)
- input the data averaging to 1 second
- interpolate az positions to center of data records.
- Create bandpass correction
- compute total power of each spectra.
- compute median of spectra that belong to the lowest 20% of
the tp above.
- fit a linear polynomial and 35th order harmonic to the
median bandpass. use this as the bandpass correction.
- divide each 1 second spectra by the bandpass correction
- compute the median of each 1 sec spectra and remove it (this
is to get rid of continuum sources).
The images show the dynamic spectra for the Clockwise (CW) and
counter clockwise (CCW) az swings for each 172 MHz band.
Birdie power vs azimuth.
Birdies were identified by looking at the
dynamic spectra. The avg power over the birdie bandwidth was
computed and then plotted vs azimuth. The clockwise and counter
clockwise swings were over plotted to see if the birdies repeated
in azimuth (for this to happen then need to be stable in time).
The plots show the birdie
power vs azimuth (.ps) (.pdf)
- Page 1: large birdies vs azimuth
- The frequency range for each birdie is printed on the right
- an offset has been added for display
- Page 2: this shows birdies with smaller amplitude vs azimuth,.
- Page 3: Esteban's rfi. Average spectra for each az swing.
- The plot shows the average spectra for the CW (black) and
CCW (red) azswings for the frequency range 6020-6040Mhz.
- Esteban reported rfi around his line at 6030 Mhz.
- The dynamic spectra showed rfi with a 10 Mhz bandwidths
centered at 6030.
- This spectral shape looks like an ofdm transmitter
- The spectra is made up of a number of channels with
carriers every few channels.
- The center is missing and has a carrier,.
Birdies with no az dependence:
- Large birdies:
- 6876-6876: does not repeat in azimuth. spike at 260 in one
swing, but not in the other
- Small birdies:
- 6961-6962.. some of this repeats, some doesn't. may be
more than one thing
Birdies with common azimuth dependence
- 6241-6271 and 6580-6609
- 6051-6076 and 6022-6046(sm)
- 6024-6046 and 6025-6034.. these overlap in freq . probably
two birdies here.
- 6563-6565 and 6628-6631
- 6742-6747 and 6850-6858